BACKGROUND

• Rana boylii provide a unique link with hydroclimatic change as their breeding phenology is tightly coupled with river hydrology. They have evolved strong breeding associations with changes in flow associated with rain or snowmelt cues in the spring.
• As one of the only obligate stream-breeding frogs in western North America, the foothill yellow-legged frog (Rana boylii Baird 1854) historically occurred in streams and rivers from Oregon to northern Baja California west of the Sierra-Cascade crest across a range of elevations from sea level to ~1400 m.
• Rana boylii have declined over 50% from the species former range (Davidson et al. 2005, Lind 2005). Many existing populations are small.
• Small populations with limited genetic diversity may have reduced adaptive potential and difficulty responding to future environmental change. Identifying these populations is crucial for effective conservation prioritization and management.

KEY QUESTIONS

1. Can we better characterize range-wide genetic structure of R. boylii, and identify areas for prioritization?
2. Has river (flow) regulation reduced connectivity and genetic health (diversity) of R. boylii?
3. Can we quantify this genetic signature for specific hydrologic flow regimes?

Flow Regimes

• Different flow regimes exihibit different patterns of magnitude, duration, frequency, and variability.
• These components can be quantified in many different ways.
• Foothill yellow-legged frogs have cued in on specific periods of the hydrograph to spawn, typically the spring snowmelt/rain recession.

Flow Seasonality and Predictability shifts with flow regulation.

• Using flow data coupled with wavelet analysis and Colwell’s M/P metric of seasonality has been shown to be a useful way to compare the inter and intra-annual changes in flow regimes (Tonkin et al. 2017).
• Strong patterns of seasonality (within-year) and predictability (among-years) can be observed in unregulated rivers (Figure A).
• Using data from USGS gaging stations, I ran a similar analysis looking at many years of flow data before and after dams were built in the Yuba and American Rivers
• We can see significant shift in seasonality in rivers that are regulated (Figure B).

RADSeq/Rapture is flexible and cost efficient

• Able to sequence thousands of samples by multiplexing at once (high throughput)
• The basic steps are:
  • Digest with Sbf1
  • Add RAD adapters
  • Sonicate/shear
  • Purify
  • Add/select specific capture baits/loci of interest

Using magnetic nanobeads to wash/extract DNA

PCA of SNPs

• The unregulated NFA shows very little genetic population structure, with a pattern indicating the population is largely mixed and/or connected.
• Compared to the MFA, which shows a strong division between tributary sites in the hydropeaking reach vs. sites upstream of the hydropeaking reach (in bypass or unregulated locations).

F_ST shows elevated patterns of genetic diversity loss

• Regulation type was shown to be more important in explaining F_ST than geographic distance (or river distance).
• The higher F_ST values observed in populations in regulated rivers indicates more limited connectivity and divergence or loss of genetic variation.
• The figure shows the mean river distance and F_ST distance for each site (so the mean of that site when measured against every other site within the river basin, cross watershed distances were not compared).